1. Field of the Invention
The present invention relates to an electromagnetic switch utilized for a starter that starts an engine, and particularly to the structure of the terminal unit thereof.
2. Description of the Related Art
In general, a starter for starting an engine is provided with a starter motor for generating torque, a speed reducer that utilizes an epicyclic gear so as to reduce the rotation speed of the rotor of the starter motor and output the torque, an overrunning clutch provided on an output axle of the epicyclic speed reducer, a pinion that is provided on the output axle along with the overrunning clutch slidably, and a shift lever that slides the overrunning clutch and the pinion along the output axle.
In addition, an electromagnetic switch for a starter is provided in the starter in an integrated manner. The electromagnetic switch for a starter includes an electromagnetic coil that is energized when the key switch of an vehicle is turned on, a plunger that is driven by electromagnetic force exerted on the electromagnetic coil when the electromagnetic coil is energized and travels so as to move the overrunning clutch and the pinion toward a ring gear of the engine, a pair of fixed contacts that are spaced apart from each other and connected with a battery and the starter motor, respectively, and a movable contact that is driven through the travel of the plunger and makes contact with the pair of fixed contacts so as to make a short circuit across the pair of fixed contacts.
The movable contact and the pair of fixed contacts are contained in a switch cap made of an insulative material. The pair of fixed contacts are connected, respectively, with a battery terminal that penetrates the switch cap from inside toward outside and a motor terminal that penetrates the switch cap from inside toward outside. On the outer surface of its axis-direction closed end, the switch cap is provided with a diaphragm disposed between the battery terminal and the motor terminal; a sufficient creepage distance between the battery terminal and the motor terminal is ensured through the diaphragm (e.g., refer to Japanese Patent Application Laid-Open No. 2004-19601).
FIG. 6 is an elevation view of a terminal unit of the foregoing conventional electromagnetic switch for a starter; FIG. 7 is a cross-sectional view of the terminal unit in FIG. 6 in the case where the cross section taken along the line A-A is viewed along the arrow A. As illustrated in FIGS. 6 and 7, a battery terminal 8 and a motor terminal 11 are fixed in a cylindrically formed switch cap 7 in such a way as to penetrate the closed portion that is one end of the switch cap 7 in the axis direction thereof. A battery terminal strip 9 connected with a battery cable 10 and a motor terminal strip 13 connected with a motor lead 14 are connected with the battery terminal 8 and the motor terminal 11, respectively, at the outside of the switch cap 7. Additionally, a battery fixed contact 8a and a motor fixed contact 11a are adhered and electrically connected to one end of the battery terminal 8 and one end of the motor terminal 11, respectively.
Between the battery terminal 8 and the motor terminal 11, there is situated a diaphragm 70 that is formed on the outer surface of the closed end of the switch cap 7; thus, as described above, a sufficient creepage distance between the battery terminal 8 and the motor terminal 11 is ensured. A wall face 7a, of the diaphragm 70, that faces the battery terminal 8 and a wall face 7b that faces the motor terminal 11 are formed in a concave shape. In some cases, the wall faces 7a and 7b of the diaphragm 70 are formed in a planar shape.
The conventional electromagnetic switch for a starter is configured in such a way that the wall face 7a, of the diaphragm 70 of the switch cap 7, that faces the battery terminal 8 is formed in a planar shape; therefore, in the case where the electromagnetic switch is installed in a vehicle in such a way that the battery terminal 8 is disposed approximately immediately above the motor terminal 11, the wall face 7a of the diaphragm 70 is likely to have a water puddle, due to a flood or the like; accordingly, under such a crucial environment as being intermittently flooded with water for a long time period, there has been a problem that the water puddle overflows into a place between the battery terminal 8 and the motor terminal 11, whereby a leakage circuit, from the battery terminal 8 or the battery terminal strip 9 to the motor terminal 11 or the motor terminal strip 13, is liable to be formed via the diaphragm 70 of the switch cap 7.
Because, from the view point of production through molding a synthetic resin, there exists restriction, which depends on the wall thickness of the diaphragm, on the longitudinal (height) dimension of the diaphragm 70 of the switch cap 7 from the side end surface of the switch cap 7, the diaphragm 70 cannot be elongated to a dimension longer that a predetermined length; in contrast, because being formed of a member the same as the member that is formed in a relatively elongated shape and forms the battery terminal 8, the motor terminal 11 with which the motor terminal strip 13 is connected is formed in a relatively elongated shape, as is the case with the battery terminal 8. Accordingly, as illustrated in FIG. 7, the respective front ends of the battery terminal 8 and the motor terminal 11 that are formed in a relatively elongated shape protrude over the front end of the diaphragm 70 of the switch cap 7, whereby there exists a region where the diaphragm 70 is not situated between the respective front ends of the battery terminal 8 and the motor terminal 11. As a result, there has been a problem that, under such a crucial environment as being intermittently flooded with water for a long time period, a water puddle due to the flood adheres to a place between the battery terminal 8 and the motor terminal 11, whereby a leakage circuit, from the battery terminal 8 to the motor terminal 11 via the diaphragm 70 of the switch cap 7, is liable to be formed.